Prevention of floor erosion of a solution mining cavity



Sept.. 5, 1967 E. P. HELVENSTON 3,339,978

PREVENTION OF FLOOR EROSION OF A SOLUTION MINING CAVITY Filed May 14,1965 s Sheets-Sheet 1 2'\- EFFLUE'NT sou/aw ROCK, SHALE, ETC.

PRODuoT MINERALS EFF LUE NT SOLVENT PRoOuc'r MINERALS IN VEN TOR EDWARDB {151. VENSTU/V @h-swh ATTOR NEYJ 'NON- Peoouo-r MINERALQ Sept. 5, 1967E. P. HELVENSTON 3,339,978

PREVENTION OF FLOOR EROSION OF A SOLUTION MINING CAVITY Filed May 14,1965 5 Sheets-Sheet 2 vSOLVENT EFFLUENT RO K, SHALE, ETC.

PRO DU CT ROCK, SHALE, are.

PEQDU cT MINERALS IN VENTOR NON- PzoDucT MINERALS row/area BHELVENSTON(914M33 g m ATTORNEY P 1967 E. P. HELVENSTON 3,339,978

PREVENTION OF FLOOR EROSION CF A SOLUTION MINING CAVITY Filed May 14,1965 5 Sheets-Sheet 5 goclc, SHALE,'ETC.

PRODUCT MINERALS NON- PaonucT MINERALS FIG. 5

INVENTOR EDWARD R HELVENSTON BY flaw SW ATTORNEYS United States atetfifiee 3,339,978, Patented Sept. 5, 1967 ABSTRACT OF THE DISCLOSUREInert particulate material such as gravel is introduced to a solutionmining cavity to form a protective layer on the floor of the cavity. Thelayer serves to insulate the floor from extraction by cavity solution.

This invention relates to a novel method of solution mining. It moreparticularly relates to guarding against extraction of the floor of asolution mining cavity.

In the solution mining of a soluble, techniques are employed whereby oneor more cased bore holes are provided through the earth to communicatewith a soluble deposit. The deposit typically comprises productminerals, i.e., minerals which it is desired to recover. Solvent of themineable or product materials is passed through a bore hole into thedeposit to extract soluble materials contained therein. The resultingsolutions are withdrawn through a conduit to the surface of the earththereby establishing a cavity in the deposit. These techniques have beenemployed, for example, in solution mining sodium chloride, potassiumchloride, sylvinite, trona, borax, sulphur, and similar extractablematerials.

Product mineral deposits are often disposed adjacent extractablenon-product materials. Very often the floor of a solution mining cavitycontains extractable non-product minerals. For example, potassiumchloride-rich deposits are often disposed above and adjacent sodiumchloride deposits lean in potassium chloride. The economics of acommercial solution mining operation in such a KCl-rich stratum areadversely affected by undue extraction of the KCl-lean deposit adjacentthe cavity floor. Extraction along the cavity floor produces effluentsfrom the cavity which contain an undesirably high proportion of NaCl toKCl.

According to the instant invention, undue extraction of the floor of asolution mining cavity is inhibited, typically substantially reduced,often essentially eliminated in a very simple manner. Thus, inaccordance with the present invention, inert particulate material isintroduced to the cavity to form an insulating layer on the floorthereof. Sufficient particulate material is introduced to the cavity toprovide a physical barrier between the pool of solution in the cavityand the cavity floor. Thus, the cavity floor beneath the inertparticulate material is protected from the extracting action of thesolution in the cavity. It is unnecessary for the improvement of thisinvention that the entire floor be covered with a layer of inertparticulate material. The improvement results when a relatively smallpercentage, sometimes no more than about 5 percent of the flgor is socovered. In small cavities a higher percentage, e. g., -50 percent ispreferable.

The particulate inert materials contemplated by the instant inventioninclude any solid material in particulate, granular, comminuted or otherdivided form which is substantially inert to and more dense that thesolution in the cavity. Relatively coarse materials are generallyeffective because they are unlikely to wash from position due tocurrents within the pool of cavity solution. The specific gravity of thematerials employed in the practice 'of this invention need not beappreciably greater than the cavity solution although heavy materialsare preferred. In solution mining operations wherein the cavity solutiontypically has a density of between about 1.1 and 1.25 grams per cubiccentimeter, particulate materials with specific gravities of betweenabout 2 and about 5 are generally employable. Heavier materials are evenbetter.

Typical of the materials contemplated by this invention are sand,gravel, pebbles, slag, cinders, crushed rock, or admixtures of thesematerials. Ungraded materials generally provide a less porous layer.Thus, the coarser particles tend to entrap the finer particles in theinterstices between the coarse particles thereby holding them in place.Even if a large quantity of fines or slimes is introduced along with theparticulate materials contemplated by this invention, the coarserparticles tend to settle to the bottom of the cavity. The slimesfrequently flush away and are removed with the efiluent from the cavity.

The invention is more readily understood with reference to theaccompanying drawings. FIGURE 1 represents a typical solution miningcavity communicating with a concentric system of conduits extendingthrough a single bore hole. FIGURE 2 represents a similar cavity inwhich the floor is protected in accordance with this invention. FIGURE 3illustrates a cavity communicating with a plurality of bore holes.FIGURES 4 and 5 represent preferred embodiments.

Referring to FIGURE 1 of the drawings, there is depicted a solutionmining cavity 8 in a mineable or product deposit. Solvent is introducedthrough the annulus between casing 1 and pipe 2. Efliuent is withdrawnthrough pipe 2. Oil pad 6 floats on top of the solution in the cavity toinsulate the roof of the cavity from undue vertical extraction. In thisfashion, horizontal development of the cavity is encouraged. The floorof cavity 8 contacts extractable non-product minerals. Due to therelatively rapid rate of fluid flow in the cavity adjacent efiluent pipe2, a portion 10 of the floor tends to be extracted. Extraction of thefloor is normally deleterious to the quality of the efiluent.

In the practice of this invention, as illustrated by FIG- URE 2,particulate material is introduced to the cavity to provide a pile orlayer 3 on the floor of the cavity. Sometimes sufiicient inertparticulate material is introduced so that insulating layer 3 covers theentire floor of the cavity. Layer 3 should contain sufiicient materialto significantly inhibit extraction of the cavity floor by the cavitysolution. Usually a layer covering only a portion, typically as littleas about 5 percent, of the cavity floor enhances the quality of theefliuent from the cavity. The precise amount of materials necessary toform an adequate protective layer depends upon a variety of factors suchas the size distribution of the particulate materials, the porosity ofthe layer, the flow rates of the currents in the pool of cavitysolution, the chemical and physical properties of the deposit, etc.Usually, a depth of as little as about A to about 6 inches of theinsulating materials contemplated by this invention effectively inhibitsextraction of the cavity floor.

This invention includes within its scope providing any effective amountof particulate materials to the cavity to establish and maintain asignificant insulating layer. The term effective amount includes anyamount sufiicient to desirably enhance the quality of the efliuentrecovered from a cavity. Although the entire cavity floor need not becovered, it is desirable to cover a substantial portion of the cavityfloor surrounding the axes of the bore holes communicating therewith.Thus, according to a preferred embodiment of this invention, sufiicientmaterial is introduced to establish an effective insulating layerextending in all horizontal directions from the axes of the bore holesto a distance of from about 5 to about 30 feet, preferably at leastabout feet. It is particularly desirable to provide such a layer on thecavity floor beneath conduits which terminate close to the cavity fioor.Thus, in a typical solution mining cavity, it is particularly desirableto insulate the floor beneath the effluent conduits.

Referring to FIGURE 3, an embodiment of the instant invention isillustrated wherein a cavity 18 communicates with a plurality of boreholes. Insulating layer 13 is provided beneath infiuent casing 11 andlayer 14 is provided beneath effluent casing 12. Oil pad 16 insulatesthe roof of the cavity from extraction. The particulate materials ofthis invention are readily introduced to a cavity through one or moreconduits communicating therewith. According to a preferred embodiment,insulating materials are introduced through all communicating bore holesto facilitate good distribution over the cavity fioor.

A noteworthy characteristic of the instant invention is the beneficialprotection of substantially the entire cavity floor provided by aninsulating layer which covers a relatively small portion thereof.Although the mechanism of this improvement is not fully understood, andwhile it is not intended to limit this invention to any particulartheory, the following is offered by way of a possible explanation. Assolvent extracts minerals from a deposit, it usually becomes more dense.The dense solution tends to settle to the bottom of the cavity fillingany low spots. Thus, dense solution settles into exposed floor areas orpockets formed in the floor by extractive action such as thosedesignated 5 in FIGURE 2 and in FIGURE 3. Solution in these pockets isthought to be relatively undisturbed by currents in the cavity. It thuseventually reaches equilibrium with the materials in the cavity floor,i.e., it becomes incapable of extracting further material from thefloor. Similarly concentrated solution becomes entrapped in theinterstices of the inert layers 3, 13 and 14, thereby further inhibitingextraction through these layers. In the absence of these layers,particularly in the vicinity of the withdrawal pipes, the high flowrates in that region would cause a continual disturbance and/or removalof this dense solution.

In practice, the exact distribution of insulating materials on the floorof a cavity is difficult to determine directly. The specific depths andareas disclosed herein and recited in the accompanying claims are basedon a physical model wherein the materials introduced to a cavity assumetheir characteristic angle of repose. This angle of repose is readilydetermined empirically for large heavy particles by allowing theselected material to drop freely through a restricted area into asubstantial pool of solution. The solution should have approximately thecomposition of the effluent from the cavity. Thus, the approximate areaand depth of material in contact with the cavity floor can be calculatedfrom the weight of material charged to the cavity.

It is recognized that the actual configuration of the insulating layerin the cavity may differ substantially from the assumed model. Thedistribution of sand, for example, which is the preferred material, willdepend more on the variable path of descent through the cavity solutionand the depth of the cavity than on the angle of repose, The model isnevertheless useful if it is desired to introduce the minimum requiredamount of particulate materials to the cavity. Due to the low cost andgeneral availability of the insulating materials contemplated by thisinvention, it is often more convenient to simply charge substantialquantities, for example, several tons, of inert particulate materialsthrough one or more conduits communicating with the cavity. Liquid,typically solvent or cavity solution, may then be introduced through thesame conduit or conduits at flow rates substantially higher than thenormal flow rates employed in the operation of the cavity. In thismanner, the insulating material is flushed out away from the conduit orconduits.

A suitable insulating layer is thus distributed over substantialportions, often the entire cavity floor. The procedure can be repeatedas often as necessary to achieve the desired results.

FIGURES 4 and 5 illustrate two embodiments of this invention whereby thelateral distribution of the insulating materials is increased. Accordingto the embodiment of FIGURE 4, a deflecting cone 7 is attached to a pipe22 and inserted through casing 21 to a cavity 28. Insulating material,for example, ungraded sand is introduced through pipe 22. FIGURE 5 showsthe same arrangement with rotating right angle nozzles 9 replacing thedeflecting cone 7. The particulate materials may be introduced to pipe22 in dry form or in a fiuid vehicle. It is often advantageous tointroduce these materials under substantial pressure to enhance thescattering effect of the inclined surface 7 or the nozzles 9. Of course,numerous other scattering techniques will become apparent to the skilledart.

Sometimes when high flow rates are employed, some of the particulateinerts may flush out of the cavity with the efiluent. In that event, itis often advantageous to introduce a compensating amount of particulateinerts with the infiuent.

The following example further illustrates the manner in which thisinvention may be practiced.

Example A solution mining operation similar to that illustrated byFIGURE 3 of the drawings is conducted in a sodium chloride deposit. Thedeposit consists of a plurality of strata of varying compositions. Themineable stratum contains in excess of about 15 percent potassiumchloride based upon the total weight of potassium chloride and sodiumchloride in the stratum. The combined Weights of potassium chloride andsodium chloride in the entire deposit are in excess of percent of theweight of the deposit. Disposed beneath the mineable stratum is a sodiumchloride-rich potassium chloride-lean stratum which contains less thanabout 10 percent potassium chloride. The area of the cavity floor iscalculated according to well known sonar techniques to be about 8,000square feet. The cavity is initially operated in accordance withaccepted solution mining practice. The effiuent from the cavity isanalyzed. It is found that the weight ratio of KCl to NaCl in theefiiuent is less than the corresponding ratio which exists in themineable stratum. Approximately 10 tons of ungraded sand are introducedto the influent casing. Approximately 10 tons of the same material areintroduced to the effluent casing. The bulk density of the sand isapproximately 90 pounds per cubic foot. The specific gravity of thedensest solution in the cavity is approximately 1.23. The sand hasapproximately the following size distribution:

Percent retained Screen size, No.: (cumulative) 4 2 8 15 16 35 3O 55 5O79 97 After introduction of the sand to the cavity, the operation of thecavity is commenced. After a period of ten days, effiuent is againcollected and analyzed. It is found that the ratio of KCl to NaCl in theefiiuent has increased.

While the instant invention has been described with reference tospecific details of certain preferred embodiments thereof, it is notintended thereby to limit the scope of the invention except insofar asspecific details are recited in the appended claims.

I claim:

1. The method of inhibiting extraction of solubles adjacent the floor ofa solution mining cavity which comprises introducing to the cavitysufiicient particulate substantially inert materials more dense than thecavity solution to form a protective layer on the floor of the cavity.

2. The method of protecting the extractable floor of a solution miningcavity from extraction by the cavity solu tion which comprisesestablishing an insulating layer on the floor of the cavity byintroducing to the cavity an effective amount of substantially inertparticulate material more dense than the cavity solution.

3. The method of claim 2 wherein the particulate material is ungradedsand.

4. The method of inhibiting extraction of the extractable floor of asolution mining cavity which comprises providing to an efiluent conduitcommunicating with the cavity suflicient inert particulate material moredense than the cavity solution to form an insulating layer of saidmaterial extending in all horizontal directions trom the aXis of theconduit for a distance of at least 5 feet.

5. The method of claim 4 wherein suflicient inert particulate materialis provided to all bore holes communicating with the cavity to establishan insulating layer extending all horizontal directions from the axes ofsaid bore holes fora distance of at least 5 feet.

6. The method of inhibiting extraction of the extractable fioor of asolution mining cavity which comprises providing to the cavitysufiicient inert particulate material more dense than the cavitysolution to establish an insulating layer adjacent at least about 5percent of the area of the floor.

7. The method of claim 6 wherein after the said layer is established,suflicient additional particulate inert material is introduced with theinfluent to the cavity to maintain said insulating layer adjacent atleast about 5 percent of the area of the cavity floor.

8. A method of increasing the ratio of product minerals to non-productminerals in the eflluent from a solution mining cavity disposed adjacenta mineable deposit and above a extractable non-product stratum whichcomprises introducing inert particulate material more dense than thecavity solution to the cavity to insulate the cavity floor fromextraction.

9. The method of claim 8 wherein the product mineral is potassiumchloride.

10. The method of claim 9 wherein the non-product stratum is rich inNaCl and lean in KCl.

References Cited UNITED STATES PATENTS 2,822,15 8 2/1958 Brinton 299-42,890,755 6/1959 Eurenius et a1 2995 X 3,088,717 5/1963 Myers 299-5ERNEST R. PURSER, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,339,978 September 5, 1967 Edward Phelps Helvenston pears in the abovenumbered pat- It is hereby certified that error ap Patent should read asent requiring correction and that the said Letters corrected below.

Column 5, line 22, before "all" insert 1n Signed and sealed this 5th dayof November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents

1. THE METHOD OF INHIBITING EXTRACTION OF SOLUBLES ADJACENT THE FLOOR OFA SOLUTION MINING CAVITY WHICH COMPRISES INTRODUCING TO THE CAVITYSUFFICIENT PARTICULATE SUBSTANTIALLY INERT MATERIALS MORE DENSE THAN THECAVITY SOLUTION TO FORM A PROTECTIVE LAYER ON THE FLOOR OF THE CAVITY.